1. Field of the Invention
The present invention relates to a plasma processing apparatus. More particularly, the present invention relates to an assembly of confinement rings of a plasma treatment apparatus.
2. Description of the Related Art
Plasma treatment apparatuses are widely used in the manufacturing of semiconductor devices for forming thin films on substrates and then etching the thin films to form patterns, such as circuit patterns. A typical plasma treatment apparatus generally includes a process chamber in which the substrate is processed, and an upper electrode and a lower electrode disposed in the process chamber. Plasma is formed between the upper electrode and the lower by impressing an RF power across the electrodes while injecting a process gas between the electrodes. The plasma treatment apparatus also includes confinement rings disposed in the process chamber around the space into which the process gas is injected. The confinement rings serve to confine the plasma so that the substrate will be processed, e.g., etched, efficiently by the plasma.
FIG. 1 shows a portion of a confinement ring assembly of a conventional plasma treatment apparatus. A cam ring 20 of the assembly is disposed above a cover of the process chamber 10. A driving means, namely a motor, is connected to the cam ring 20 so as to selectively rotate the cam ring 20. The confinement ring assembly also includes a plurality of plungers that are spaced from each other by equal angular intervals about the process chamber 10 and cooperate with the cam ring 20.
More specifically, the plungers (only one of which is shown) each comprise a roller 30 that contacts the cam ring 20 along the bottom (cam) surface of the cam ring 20. The roller 30 is thus moved upwardly or downwardly by the bottom surface of the cam ring 20 when the cam ring 20 is rotated by the motor. The axle of each roller 30 is fixed to a bearing block 40 such that the bearing block 40 moves vertically along with the roller 30.
The plungers also each comprise a rod 50, a cylinder 60 and a spring 61. The upper end of the rod 50 is engaged with the lower portion of a bearing block 40 so as to move therewith. The spring 61 is disposed within the cylinder 60. More specifically, a quad seal and an O-ring are mounted to the cylinder 60 within the lower end portion of the cylinder 60. The spring 61 surrounds the rod 50 above the quad seal and the O-ring and is interposed between the quad seal and a flange that is fixed to the rod 50. Thus, the spring biases the rod 50 upwardly and hence, the roller 30 is biased into engagement with the cam ring 20.
Furthermore, each plunger also includes a bushing 62 fitted to the lower portion of the cylinder 60. The rod 50 extends freely through the bushing 62 such that the rod 50 may move vertically relative to the bushing 62. A quartz ring 70 is engaged with the outer peripheral surface of the bushing 62 of each plunger. An upper confinement ring 80 is engaged with the bottom of the quartz ring 70 and is held in place by the bushings 62 such that the upper confinement ring 80 can not be separated from the quartz ring 70. A lower confinement ring 90 is coupled by nuts, for example, to the lower ends of the rods 50 under the upper confinement ring 80. Thus, the lower confinement ring 90 can be raised and lowered by the rods 50. The quartz ring 70, the upper confinement ring 80, and the lower confinement ring 90 generally have the same or similar inner and outer diameters, respectively.
The total number of confinement rings in the process chamber depends on the manufacturer. Regardless, as shown in FIG. 2, the confronting surfaces of the conventional confinement rings 80 and 90 are spaced from each other by a predetermined interval. Therefore, some of the plasma penetrates into this gap between the confinement rings 80 and 90, thereby sharply lowering the efficiency of the process.
Furthermore, a polymer byproduct of the plasma process accumulates on the side wall surfaces of the confinement rings 80 and 90. However, the side wall surfaces of the confinement rings 80 and 90 are not large enough for the polymer to adhere well to. Therefore, the polymer readily flakes off of the confinement rings 80 and 90 and thus, is a source of particulate contamination, i.e., lowers the quality of the product.